Which excerpt from "On Becoming an Inventor" by Dean Kamen expresses a fact rather than an opinion?

a) Kamen believes it may change the way people move around in crowded cities . . .

b) I took the pictures, though somewhat reluctantly. I didn't like the blood.

c) At college I was struck by how smart the teachers were—in electronics, in physics, and in mathematics.

d) I didn't officially graduate from Worcester Polytechnic Institute until years later when I was awarded their honorary Ph. D.